Numerical simulation plays an important role in the study of structure formation of the universe. However, the mass resolution in current simulations is still poor. Due to technical difficulties, it is necessary to use both greatly reduced number density of particles and greatly raised unit particle mass. Consequently, the particle masses used in cosmological simulations are about $10^{70}$ times larger than the $Gev$ candidates in particle physics. This is a huge physical bias that cannot be neglected when interpreting the results of the simulations. Here we discuss how such a bias affects Cold Dark Matter (CDM) cosmological simulations. We find that the small scale properties of the CDM particle system are changed in two aspects. 1) An upper limit is imposed on the spatial resolution of the simulation results. 2) Most importantly, an unexpected short mean free path is produced, and the corresponding two body scattering cross section is close to the value expected in the Self-Interaction Dark Matter(SIDM) model. Since the mean free path of real CDM particle systems is much longer than that in the simulations, our results imply 1) that there is probably no 'cusp problem' in real CDM halos, and 2) that a much longer time is needed to form new virialized halos in real CDM particle systems than in the simulations. This last result can help us understand the 'substructure problem'. Our discussion can also explain why the massive halos in the simulations may have smaller concentration coefficients.Comment: 4 pages,no figures. Submitted to ApJ

This vitro study aimed to evaluate the effects of 45S5 bioactive glass (BAG) and Er: YAG laser as desensitization treatments on the microtensile bond strength (MTBS) of fluorosed teeth. The 120 noncarious fluorosis were to obtain superficial dentin, being classified into four groups according to the Thylstrup and Fejerskov Index (TFI). Specimens from each group were randomly divided into five subgroups. After fluorosed teeth hypersensitivity models were established, the following pretreatments were applied on dentine surface: Subgroup 1: deionized water (Control); Subgroup 2: BAG; Subgroup 3: Er:YAG laser; Subgroup 4: BAG + Er:YAG laser, and Subgroup 5: Er:YAG laser + BAG. One sample was randomly selected from each subgroup for scanning electron microscope (SEM). The remaining samples were bonded with composite resin by Adper Single Bond 2 adhesive. Then water bath at 37 C for 24 hr. After 5,000 thermocycling, MTBS was tested and fracture mode was analyzed. The difference of MTBS between BAG group and Control group was found statistically significant (p < .05) in fluorosis. The Er:YAG laser + BAG group showed lowest MTBS values in fluorosis. In conclusion, the pretreatment of BAG might be beneficial to the adhesive of fluorosed teeth. Er:YAG laser desensitization alone or using BAG first and then Er:YAG laser desensitization might not affect the adhesive of fluorosed teeth, while Er:YAG laser desensitization followed by the pretreatment of BAG would be not conducive to the adhesive of fluorosed teeth.

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The study evaluated the effect of sodium hypochlorite (NaOCl) treatment on fluorotic enamel bonding of four adhesive systems. They were Single Bond 2 (SB2), Prime&Bond NT (PBN), Clearfil SE Bond (CSB), and Single Bond Universal (SBU). One hundred eighteen extracted moderate fluorotic molars were divided into eight groups according to NaOCl pretreatment and four adhesive systems. The microshear bond strength (μSBS), etching pattern, and penetration depth (PD) were observed. The statistical method was two-way ANOVA and least significant difference (LSD) test (α=0.05). The application of NaOCl significantly increased the μSBS of PBN and SBU (p<0.05). The enamel-etching pattern of CSB and SBU was deeper under SEM. A noticeable increase of PD was in SB2 and SBU after the application of NaOCl (p<0.05). Pretreatment of 5.25% NaOCl for the 60 s can increase μSBS of PBN and SBU, PD of SB2 and SBU, and improve enamel-etching pattern of CSB and SBU to fluorotic enamel.

The aim of this in vitro study was to estimate the effect of the species concentration of 45S5 bioactive glass (BAG) used as pretreatment on the microshear bond strength (MSBS) of dental fluorosis (DF). Based on the Thylstrup and Fejerskov index, 80 teeth were randomly divided equally into four groups: TFI 0, sound dentin; TFI 1–3, mild fluorosis; TFI 4–5, moderate fluorosis; and TFI 6–9, severe fluorosis. Each group was randomized into five subgroups. After preparing the dentin hypersensitivity model of DF, the dentin was pretreated as follows, Subgroup 1: deionized water (Control group); Subgroup 2: 1% BAG; Subgroup 3: 5% BAG; Subgroup 4: 10% BAG, and Subgroup 5: 20% BAG. Stochastically one specimen was selected from each subgroup for scanning electron microscope and energy dispersive spectrometer analysis. After being made of resin–tooth bonding samples, the remains were in water bath at 37 °C for 24 hr. Subsequently, samples from each subgroup were randomly selected to test MSBS without aging, or after a thermocycle of 5,000 and 10,000 times, respectively. The fracture modes were analyzed. Compared with the group of 1% BAG and Control, the exposure area of tubules in 5%, 10%, and 20% BAG group had significant difference (p < .05). MSBS results indicated that there were significant differences between 10% BAG with other groups. The 20% BAG group showed the lowest MSBS among all groups. Pretreatment of 10% BAG solution may be conductive to enhance the bond strength of DF, while 20% BAG solution adversely.